5 Dark matter and dark energy, the Universe revealed

Transcription

1 5 Dark matter and dark energy, the Universe revealed

2 Our place Courtesy: NASA

3 How much matter? Add up all we can see ~ 1 atom per 10 m -3 Ω = 1? ~ 1 atom m -3 Dark matter MACHOS WIMPS The quintuplet cluster, courtesy NASA

4 What s in the dark? We can t see everything Dark matter in silhouette Dark matter feels the force of gravity NGC 3314, courtesy NASA:

5 Newton s law of Gravity Every little bit of mass in the Universe attracts every other bit with a force The force of attraction between two masses m 1 and m 2 is proportional to the product of the masses and the inverse square of the distance d between them F m m = G G d s 2, = m kg 2 attraction m 1 m 2 a sphere attracts like a point mass located at its centre

6 Mass in a galaxy Courtesy ukdmc UK dark matter collaboration

7 NGC 3198 Courtesy: NGC 3198 Stars only extend to 10 kpc Radio doppler shift shows flat rotation to 30+ kpc

8 More evidence M L galaxies = 20 M L Sun Galaxies have a high mass to luminosity ratio

9 MACHOS Massive Compact Halo Objects candidates: red dwarves brown dwarves white dwarves VMOs very massive objects SMOs super massive objects cold clouds of mainly hydrogen primordial black holes none of these account for all the missing mass

10 23% of energy is dark matter Most of it is not baryonic WIMPS Weakly Interactive Massive Particles NGC 4412 courtesy NASA:

11 Boulby mine Dark matter wimp search source: UKDMC /ukdmc.html

12 Any more ideas? Schematic of a spiral galaxy if we include dark matter Are WIMPS supersymmetric particles? Source:

13 Anglo Australian 2dF galaxy survey

14 Part of the map of the Universe The structure of the universe every dot a galaxy Part of the Sloan Survey of distant galaxies from z 0.05 to z 0.5 Courtesy: /p0.300.gif

15 Galactic clustering Clustering of mass is driven by gravity Explanation of clustering is a major goal of modern astronomy Galaxies abound courtesy NASA jpg

16 Dark Energy Accelerating expansion of the universe CosmoΛogical constant Λ is negative 1 = Ω 0 = Ω m + Ω Λ surely Ω is exactly 1? zero energy in the Universe! There are no good candidates for dark energy a fluid quintessence vacuum energy Illustration source:

17 Our Universe Ω 0 = 1.02 ± 0.02 Ω m = 0.27 ± 0.04 Ω b = ± Ω r = Ω ν <0.015, Ω Λ = 0.73 ± 0.04 q 0 = ±0.02 t 0 = 13.7 ± 0.2 Gyr baryons/photons is (6.1 ± 0.7) m neutrinos <0.23 ev CMB z = 1088 ± 1 NGC 1316 courtesy NASA: /images/a/formats/large_web.jpg

18 Clustering of mass How did the universe progress from a few atoms m -3 to matter as we know it at atoms m -3? Galactic spatial density survey covering 2 million galaxies over an extensive part of the southern sky Courtesy: Oxford APM survey

19 Clues to galaxy formation Metallicity (Fe observed in a star s spectrum) is a clue to density and age of surroundings of stars Halo stars have low metallicity hot dark matter and cold dark matter scenarios predict different populations of low metallicity stars Distribution and velocity surveys are needed to mine the history of our galaxy

20 Mapping dark matter Develop the galactic rotational velocity idea to get more detailed velocity information for a much larger range of stars and structures 10 km s milli-arc sec y -1 at 25,000 LY Hipparcos survey set the scene for milliarc second positional surveys. Image source ESA objectid=14060 Earth Transverse velocity Radial velocity Star

21 Our galactic history A story for the future Graphic of Milky Way galaxy courtesy NASA:

22 Classifying galaxies Edwin Hubble ( ) Edwin Hubble Elliptical E0 E7 Lenticular S0 Spiral ordinary Sa, Sb, Sc in order of decreasing spiral tightness barred SBa, SBb, SBc Irregular NGC 3384 in Leo M109, type SBc courtesy:

23 Ellipticals M60 NGC 4649 type E2 courtesy: ge_gallery/images/d6/m6 0a.jpg M49 NGC 4472 type E4 courtesy: M84, NGC4374 in the Virgo cluster, Type E1 courtesy:

24 Spirals M88, NGC4501 Type Sc in Coma Berenices Courtesy M99, NGC4254 Type Sc in Coma Berenices courtesy: g M98, NGC4192 Type Sb in Coma Berenices Courtesy: M65 type Sa Courtesy: AAO

25 NGC 1232 Sc galaxy in Eridanus source: ESO

26 M51 Courtesy:

27 Barred spirals M91, NGC4548 type SBb in Coma Berenices Courtesy: NGC 3185 type Sba Courtesy: NGC 3185 type SBc Courtesy: g

28 NGC 1365 One of the best barred spirals in the southern hemisphere Source: /phot-08a-99-preview.jpg

29 NGC 1672 Courtesy: NASA/ESA Hubble Heritage;

30 Irregular Small Magellanic Cloud Source: Large Magellanic Cloud source:

31 Hubble s tuning fork diagram Original diagram suggested an evolutionary sequence Not that simple Source:

32 Tuning fork schematic Fig. 17.7, Courtesy: Kuhn & Koupelis

33 Why spirals? Effect is not a consequence of differential rotation ~ 20 rotations around our galaxy for our Sun Spiral pattern would be lost Fig Courtesy Kuhn & Koupelis

34 Density waves Fig Courtesy: Kuhn & Koupelis